Yellowstone is blowing off a lot of helium say researches investigating the gases the geyser releases. They say this helium had been trapped under the Earth’s crust for hundreds of millions of years. More recently though, in the last couple million years that is, the old part of the crust has been being heated by a nearby volcano sleeping under the park. The pressure of a plate moving over a hot spot is pushing old rocks up and releasing helium that’s been trapped inside for a long time.